Three-dimensional photography is achieved by recording left and right eye views of a scene as two separate images. The left and right images are projected simultaneously onto a screen, typically one coated with a metallic surface. The separation between the two images is accomplished by means of polarizing filters placed in the projection beams of the left and right images with the polarizing axes set at 90  to each other and therefore cancelling each other. To ensure that each eye sees only the corresponding image the stereoscopic scene is viewed through glasses with polarizing filters whose polarizing axes are set at 90° to each other. The resultant stereoscopic image can be viewed in full color.
The stereoscopic images can be recorded by various means, for example, using two cameras set side by side (as described in U.S. Pat. No. 5,835,133) or a split lens system designed to record a stereoscopic pair of images on the same frame side by side or one image above the other. The latter scheme is known as an ‘over-under’ approach and an example thereof is described in U.S. Pat. No. 4,436,369. The pair of images may be arranged side by side, but with one image turned through 180° relative to the other image, as described in U.S. Pat. Nos. 5,357,369 and 5,727,239.
An alternative technique has been developed for cinematography whereby the discrete left and right eye images are recorded separately and sequentially on the image-recording medium, i.e. on alternate frames of a photographic film at double the normal frame rate. Such an arrangement is shown in U.S. Pat. No. 4,676,298. The images can be viewed either by projecting the images sequentially at double the normal frame rate or by simultaneously projecting both the left and right eye images through an optical arrangement that superimposes both images onto the screen. Crossed polarizing filters are placed in the projected beams of the appropriate images. The images are viewed through glasses with polarizing filters whose polarization axes are at 90° to one another corresponding to the polarization axes of the projected images.
However, in the case of the “over-under” method, where a single projection lens and additional optical arrangements are used to project both images the projection arrangement has a detrimental effect that the optical distortions introduced by the optical elements, mainly spherical aberrations tend to be exaggerated when the two images are superimposed onto each other for viewing. A perfect match between the two images is not possible on projection because each image is affected differently by the spherical aberrations of the projection lens since both images are part of the same image circle, i.e. the top corners of the upper image really match the bottom corners of the lower image instead of the corresponding corners.
It would therefore be advantageous to provide apparatus for recording and viewing three-dimensional images that has the advantages of the present known systems, but that mitigates the known disadvantages of these systems. For such an apparatus to be able to record and reproduce a stereoscopic image with a realistic depth perception, it would need to have all three of the following key elements:
a) a wide horizontal angle of view, of approximately 45° or 60°,
b) variable convergence, emulating the functions of human eyes, and
c) an inter-ocular distance corresponding to that of human eyes, the average distance in adults being 65 mm.